1. Field of the Invention
The present invention relates to a radio provided with a broad band automatic gain control circuit, and more particularly, to a radio which prevents the level of a signal transmitted from a desired broadcasting station from being suppressed by the operation of the broad band automatic gain control circuit in the presence of an interference signal.
2. Description of Related Art
A handbook entitled "SANYO'S 1985 Semiconductor Monolithic Bipolar Integrated Circuit" published on Mar. 20, 1985 describes on page 81 through 90 an IC (LA 1135) for use in an amplitude modulation (AM) tuner provided with a broad band automatic gain control (AGC) circuit. As shown in FIG. 2, as well known, the PLL 10 and the control circuit 16 are provided in microcomputers for use in synthesizers.
A radio wave received by the radio shown in FIG. 2 is converted into a sound signal, at the output terminal of the detecting circuit 9, corresponding to the radio wave signal transmitted from a desired broadcasting station. However, if an interference signal with a high level transmitted from a different broadcasting station is received in addition to the signal of the desired broadcasting station, the broad band AGC operates. As a result, the level of the signal transmitted from the desired broadcasting station is suppressed. If the intensity of the electric field of the signal transmitted from the desired broadcasting station is weak, the level of the signal transmitted from the desired broadcasting station becomes very low because the signal level is suppressed. Consequently, it is difficult to listen to the broadcasting of the desired broadcasting station.